Cold fusion is a hypothesized type of nuclear reaction that would occur at, or near, room temperature. It would contrast starkly with the "hot" fusion that is known to take place naturally within stars and artificially in hydrogen bombs and prototype fusion reactors under immense pressure and at temperatures of millions of degrees, and be distinguished from muon-catalyzed fusion. There is currently no accepted theoretical model that would allow cold fusion to occur.
In 1989, two electrochemists, Martin Fleischmann and Stanley Pons, reported that their apparatus had produced anomalous heat ("excess heat") of a magnitude they asserted would defy explanation except in terms of nuclear processes.[1] They further reported measuring small amounts of nuclear reaction byproducts, including neutrons and tritium.[2] The small tabletop experiment involved electrolysis of heavy water on the surface of a palladium (Pd) electrode.[3] The reported results received wide media attention[3] and raised hopes of a cheap and abundant source of energy.[4]
Many scientists tried to replicate the experiment with the few details available. Hopes faded with the large number of negative replications, the withdrawal of many reported positive replications, the discovery of flaws and sources of experimental error in the original experiment, and finally the discovery that Fleischmann and Pons had not actually detected nuclear reaction byproducts.[5] By late 1989, most scientists considered cold fusion claims dead,[6][7] and cold fusion subsequently gained a reputation as pathological science.[8][9] In 1989 the United States Department of Energy (DOE) concluded that the reported results of excess heat did not present convincing evidence of a useful source of energy and decided against allocating funding specifically for cold fusion. A second DOE review in 2004, which looked at new research, reached similar conclusions and did not result in DOE funding of cold fusion.[10] Presently, since articles about cold fusion are rarely published in peer-reviewed mainstream scientific journals, they do not attract the level of scrutiny expected for mainstream scientific publications.[11]
Nevertheless, some interest in cold fusion has continued through the decades—for example, a Google-funded failed replication attempt was published in a 2019 issue of Nature.[12][13] A small community of researchers continues to investigate it,[6][14][15] often under the alternative designations low-energy nuclear reactions (LENR) or condensed matter nuclear science (CMNS).[16][17][18][19]
History
Nuclear fusion is normally understood to occur at temperatures in the tens of millions of degrees. This is called "thermonuclear fusion". Since the 1920s, there has been speculation that nuclear fusion might be possible at much lower temperatures by catalytically fusing hydrogen absorbed in a metal catalyst. In 1989, a claim by Stanley Pons and Martin Fleischmann (then one of the world's leading electrochemists) that such cold fusion had been observed caused a brief media sensation before the majority of scientists criticized their claim as incorrect after many found they could not replicate the excess heat. Since the initial announcement, cold fusion research has continued by a small community of researchers who believe that such reactions happen and hope to gain wider recognition for their experimental evidence.
Early research
The ability of palladium to absorb hydrogen was recognized as early as the nineteenth century by Thomas Graham.[20][21] In the late 1920s, two Austrian-born scientists, Friedrich Paneth and Kurt Peters, originally reported the transformation of hydrogen into helium by nuclear catalysis when hydrogen was absorbed by finely divided palladium at room temperature. However, the authors later retracted that report, saying that the helium they measured was due to background from the air.[20][22]
In 1927, Swedish scientist John Tandberg reported that he had fused hydrogen into helium in an electrolytic cell with palladium electrodes.[20] On the basis of his work, he applied for a Swedish patent for "a method to produce helium and useful reaction energy".[20] Due to Paneth and Peters's retraction and his inability to explain the physical process, his patent application was denied.[20][23] After deuterium was discovered in 1932, Tandberg continued his experiments with heavy water.[20] The final experiments made by Tandberg with heavy water were similar to the original experiment by Fleischmann and Pons.[24] Fleischmann and Pons were not aware of Tandberg's work.[25][text 1][text 2]
The term "cold fusion" was used as early as 1956 in an article in The New York Times about Luis Alvarez's work on muon-catalyzed fusion.[26] Paul Palmer and then Steven Jones of Brigham Young University used the term "cold fusion" in 1986 in an investigation of "geo-fusion", the possible existence of fusion involving hydrogen isotopes in a planetary core.[27] In his original paper on this subject with Clinton Van Siclen, submitted in 1985, Jones had coined the term "piezonuclear fusion".[27][28]
Fleischmann–Pons experiment
The most famous cold fusion claims were made by Stanley Pons and Martin Fleischmann in 1989. After a brief period of interest by the wider scientific community, their reports were called into question by nuclear physicists. Pons and Fleischmann never retracted their claims, but moved their research program from the USA to France after the controversy erupted.https://en.wikipedia.org/wiki/Cold_fusion
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